C in a Nutshell

Name

gmtime

Synopsis

Converts a timer value into a year, month, day, hour, minute, second, etc.

#include <time.h>
struct tm *gmtime( const time_t *timer );

The gmtime() function converts a numeric time value (usually a number of seconds since January 1, 1970, but not necessarily) into the equivalent date and time structure in Coordinated Universal Time (UTC, formerly called Greenwich Mean Time; hence the function’s name). To obtain similar values for the local time, use the function localtime().

The function’s argument is not the number of seconds itself, but a pointer to that value. Both the structure type struct tm and the arithmetic type time_t are defined in the header file time.h.

The tm structure is defined as follows:

struct tm {
  int tm_sec;            /* Seconds since the full minute: 0 to 60 */
  int tm_min;            /* Minutes since the full hour:   0 to 59 */
  int tm_hour;           /* Hours since midnight:          0 to 23 */
  int tm_mday;           /* Day of the month:     1 to  31 */
  int tm_mon;            /* Months since January: 0 to  11 */
  int tm_year;           /* Years since 1900               */
  int tm_wday;           /* Days since Sunday:    0 to   6 */
  int tm_yday;           /* Days since Jan. 1:    0 to 365 */
  int tm_isdst;          /* Flag for Daylight Savings Time:
                            greater than 0 if time is DST;
                            equal to 0 if time is not DST;
                            less than 0 if unknown.        */
};

The argument most often passed to gmtime() is the current time, obtained as a number with type time_t by calling the function time(). The type time_t is defined in time.h, usually as equivalent to long or unsigned long.

Example

The following program ...